(1) Field of the Invention
This invention relates to the use of different transmittance light absorbing material for different duty ratio contact hole patterns and line/space patterns in attenuating phase shifting masks.
(2) Description of the Related Art
Attenuating phase shifting masks are often used to form patterns on integrated circuit wafers. As pattern dimensions become very small critical dimension proximity effect can become a significant problem and methods to correct for the proximity effect problems must be used.
U.S. Pat. No. 5,869,212 to Hashimoto describes an attenuating phase shifting mask using regions of increased light transmissivity adjacent to the defined circuit features.
U.S. Pat. No. 5,786,114 to Hashimoto describes an attenuating phase shifting mask where boundary regions are formed form the same halftone layer used to form circuit regions. The halftone layer in the boundary regions are not subjected to the stabilization step and thus have lower transmittance than the stabilized halftone layer. This lower transmittance halftone material in the boundary regions helps avoid light leakage to adjacent chip areas.
U.S. Pat. No. 5,766,806 to Spence describes a phase shift mask using different phase shift amounts in different regions of the pattern.
U.S. Pat. No. 5,783,337 to Tzu et al. describes an attenuating phase shifting mask using an opaque border.
U.S. Pat. No. 5,618,643 to Dao et al. describes an embedded phase shifting mask with a roughened surface to change the transmission.